Which credit card gives the highest cashback on online shopping?

For the fee waiver condition: most banks count only retail purchases, not EMI, wallet loads, or fuel (in some cases). Read the TnC PDF linked at the bottom of the fee-waiver email — it's usually 2-3 paragraphs of fine print that change everything.

The 'minimum due' trap is real. Banks love it because they charge ~36-42% interest on the carried-forward amount. If you can't pay the full bill this month, pay at least 50% — anything below that and the interest eats the rewards of the next 6 months.